JP5601939B2 - Piezoelectric actuator drive circuit and piezoelectric actuator device including the same - Google Patents

Description

  The present invention relates to a piezoelectric actuator drive circuit, and in particular, a piezoelectric actuator drive circuit that drives a piezoelectric actuator that includes a plurality of polarization units and that applies a drive voltage to at least one of the plurality of polarization units. The present invention relates to a piezoelectric actuator device.

  In general, a piezoelectric actuator such as a standing wave type ultrasonic motor (piezomotor) has a plurality of polarization portions formed in an integral piezoelectric element, and one or more of the polarization portions are supplied from a high-voltage power source. A voltage pulse is applied and driven. In an actuator that applies a voltage pulse to one of a plurality of polarization parts, a voltage pulse is applied to different polarization parts when the actuator is rotated forward (forward drive) and when the actuator is reversed (reverse drive). Applied. In addition, in an actuator in which voltage pulses are applied to a plurality of polarization parts, the waveforms of the voltage pulses applied to the polarization parts are different from each other, and when the actuator is rotated forward (driven in the forward direction), In the case of inversion (reverse driving), the phase relationship of each voltage pulse waveform is changed.

  Japanese Patent No. 44066952 (Patent Document 1) describes a vibration actuator. In this vibration actuator, two AC signals are input to the vibrator, and by changing the voltage or phase of at least one of these AC signals, the inclination of the axis in the locus of elliptical motion of the vibrator is changed. I have control.

Japanese Patent No. 44066952

  However, the drive device for the vibration actuator described in Japanese Patent No. 44066952 has a problem that it is difficult to drive the actuator efficiently. In addition, this vibration actuator drive device has a problem that hunting or the like tends to occur depending on the drive speed, and it is difficult to control the actuator smoothly.

  An object of the present invention is to provide a piezoelectric actuator driving circuit that can efficiently drive a piezoelectric actuator or smoothly drive a piezoelectric actuator, and a piezoelectric actuator device including the piezoelectric actuator driving circuit.

In order to solve the above-described problem, the present invention is a piezoelectric actuator drive circuit that includes a plurality of polarization units, and that drives a piezoelectric actuator in which a drive voltage is applied to at least one of the plurality of polarization units. Connected between the voltage source, the polarization unit, and the voltage source, and is connected between the high-side switching element that is switched between a conductive state and a non-conductive state by the control signal, and the polarization unit and the ground potential, and is conductive by the control signal. A low-side switching element that is switched between a state and a non-conduction state, and a voltage application that controls the high-side switching element and the low-side switching element so that only the high-side switching element is conductive and the voltage source is connected to the polarization unit The high-side switching element and the low-side switching element are both in a non-conductive state, and the polarization unit is A switching element that drives a piezoelectric actuator by applying a voltage pulse to the polarization part by periodically switching the float period that is separated and the ground period in which only the low-side switching element is in a conductive state and connecting the polarization part to the ground potential possess a control circuit, the switching element control circuit, a plurality of polarized portion, to apply a voltage pulse having different respective phases, the length of the float period include applying different voltages pulses to the polarized portion It is characterized by.

  In the present invention configured as described above, the voltage source is connected to the polarization section via the high-side switching element. On the other hand, the polarization part is connected to the ground potential via the low-side switching element. The switching element control circuit has a voltage application period in which only the high-side switching element is in a conductive state and the voltage source is connected to the polarization unit, and the high-side switching element and the low-side switching element are both in a non-conduction state. A voltage pulse is applied to the polarization section by periodically switching between a float period disconnected from the ground potential and a ground period in which only the low-side switching element is in a conductive state and the polarization section is connected to the ground potential.

According to the present invention configured as described above, since the float period is provided between the voltage application period and the grounding period, the change in the voltage applied to the polarization unit becomes smooth, and the piezoelectric actuator can be efficiently used. Or it can drive smoothly.
Further, according to the present invention configured as described above, since voltage pulses having different phases are applied to the plurality of polarization portions of the piezoelectric actuator, compared to the case where a voltage pulse is applied only to a single polarization portion, The piezoelectric actuator can be driven efficiently or smoothly.
Furthermore, according to the present invention configured as described above, voltage pulses having different float period lengths are applied to each polarization unit, so that appropriate driving can be performed according to the piezoelectric actuator to be driven. .

  In the present invention, preferably, the switching element control circuit includes a first control mode in which the voltage pulse applied to each polarization unit includes a float period having the same length, and the voltage pulse applied to each polarization unit has a different length. Switch between at least two of the second control mode including the float period and the third control mode including the float period in which the length of the voltage pulse applied to each polarization unit is changed during driving of the piezoelectric actuator. To do.

  According to the present invention configured as described above, since the first control mode and the second control mode are switched and executed, the driving situation in which the first control mode is advantageous and the driving situation in which the second control mode is advantageous are obtained. By switching the control accordingly, the piezoelectric actuator can be driven more efficiently and smoothly.

  In the present invention, it is preferable that the piezoelectric actuator is an ultrasonic motor, and the switching element control circuit executes the second control mode when the ultrasonic motor is activated, and then when the ultrasonic motor reaches a predetermined number of rotations, the switching element control circuit executes the second control mode. Switch to 1 control mode.

  According to the present invention configured as described above, after starting the ultrasonic motor in the second control mode with good startability, the startability and efficiency are improved by switching to the first control mode with good drive efficiency. Can do.

In the present invention, the float period preferably occupies 5% or more of one period of the voltage pulse to be applied.
According to the present invention configured as described above, a sufficient float period can be taken, so that the driving efficiency can be sufficiently improved.

In the present invention, it is preferable that the polarization unit further includes a coil for generating a high voltage, and the high-side switching element and the low-side switching element are connected to the polarization unit via the coil.
According to the present invention configured as described above, it is possible to apply a voltage higher than the voltage of the voltage source to the polarization part by utilizing the resonance phenomenon caused by the coil. For this reason, the piezoelectric actuator can be driven by a battery or the like.

  In addition, the piezoelectric actuator device of the present invention includes a rotor, a stator having a plurality of polarization units that drive the rotor, and a piezoelectric actuator drive of the present invention that applies a drive voltage to at least one of the plurality of polarization units. And a circuit.

  According to the piezoelectric actuator drive circuit of the present invention and the piezoelectric actuator device including the piezoelectric actuator drive circuit, the piezoelectric actuator can be efficiently driven or the piezoelectric actuator can be smoothly driven.

It is a block diagram which shows the whole piezoelectric actuator apparatus by embodiment of this invention. It is a circuit diagram and a timing chart explaining the effect | action of the A phase voltage pulse generation circuit incorporated in the piezoelectric actuator drive circuit by embodiment of this invention. It is a figure which shows each voltage pulse at the time of forward rotation and inversion of a piezoelectric actuator. It is a voltage pulse waveform when the float periods of the A phase voltage pulse generation circuit and the B phase voltage pulse generation circuit are the same. It is a voltage pulse waveform when the float period of the B phase voltage pulse generation circuit is shorter than the float period of the A phase voltage pulse generation circuit. This is a voltage pulse waveform when no float period is provided for both the A-phase voltage pulse generation circuit and the B-phase voltage pulse generation circuit shown as a comparative example. It is a graph which shows the relationship between the rotation speed at the time of rotating the rotor of a piezoelectric actuator by the piezoelectric actuator drive circuit by embodiment of this invention, and the consumption current of a piezoelectric actuator drive circuit. It is a graph which shows the relationship between the frequency of a voltage pulse waveform, and the rotation speed at the time of rotating the rotor of a piezoelectric actuator with the piezoelectric actuator drive circuit by embodiment of this invention.

Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
First, a piezoelectric actuator device according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram showing the entire piezoelectric actuator device according to the first embodiment of the present invention. FIG. 2 is a circuit diagram and a timing chart for explaining the operation of the A-phase voltage pulse generation circuit built in the piezoelectric actuator drive circuit. FIG. 3 is a diagram showing each voltage pulse at the time of forward rotation and inversion of the piezoelectric actuator.

  As shown in FIG. 1, the piezoelectric actuator device 1 according to this embodiment includes a piezoelectric actuator 2 and a piezoelectric actuator drive circuit 3 that drives the piezoelectric actuator 2. The piezoelectric actuator device 1 of the present embodiment is configured such that the rotor 6 is rotated forward or reversely by driving a plurality of polarization units provided in the piezoelectric actuator 2 by the piezoelectric actuator drive circuit 3. .

  As shown in FIG. 1, the piezoelectric actuator 2 includes polarization portions 4 a and 4 b, a friction member 5, and a rotor 6. The piezoelectric actuator drive circuit 3 includes an A phase voltage pulse generation circuit 8, a B phase voltage pulse generation circuit 10, a microcomputer 32, a D / A converter 34, a voltage control oscillator 36, and a phase shifter 38. And having.

  The polarization parts 4a and 4b are formed in a single piezoelectric characteristic member, the polarization part 4a is applied with a voltage pulse by the A-phase voltage pulse generation circuit 8, and the polarization part 4b is supplied with the B-phase voltage pulse generation circuit 10 Is configured to apply a voltage pulse. In the present embodiment, the polarization portions 4a and 4b are attached to a single piezoelectric characteristic member 4c formed in a rectangular parallelepiped shape, a ground electrode 4d attached to one surface thereof, and an opposite side of the ground electrode 4d. 4 electrodes 4e, 4f, 4g and 4h.

  The ground electrode 4d is attached to the piezoelectric characteristic member 4c so as to cover the entire surface of the piezoelectric characteristic member 4c, and is connected to the ground potential. Four electrodes 4e, 4f, 4g, and 4h are mounted side by side on the surface of the piezoelectric characteristic member 4c opposite to the ground electrode 4d. In FIG. 1, the electrode 4e arranged at the upper left and the electrode 4h arranged at the lower right are electrically connected, and the electrode 4f arranged at the upper right and the electrode 4g arranged at the lower left are electrically connected. It is connected to the. Thereby, the upper right part and the lower left part of the piezoelectric characteristic member 4c in FIG. 1 where the electrodes 4f and 4g are arranged function as the polarization part 4a, and the upper left part and the lower right part where the electrodes 4e and 4h are arranged are It functions as the polarization part 4b. In the present specification, a configuration in which a plurality of polarization portions are formed in a single piezoelectric characteristic member and a configuration in which one polarization portion is formed in each of the plurality of piezoelectric characteristic members as in the present embodiment. It will be referred to as “plurality” of polarization parts.

  As shown in FIG. 1, the polarization unit 4 a is configured to be deformed by application of an alternating voltage (voltage pulse) in the ultrasonic band from the A-phase voltage pulse generation circuit 8 and to be ultrasonically vibrated. On the other hand, the polarization unit 4b is configured to be deformed by applying an alternating voltage (voltage pulse) in the ultrasonic band from the B-phase voltage pulse generation circuit 10, and to be ultrasonically vibrated. In the present embodiment, the piezoelectric actuator 2 includes only the polarization portions 4a and 4b. However, the piezoelectric actuator drive circuit of the present invention can also be applied to a piezoelectric actuator including a large number of sets of polarization portions. .

  The friction member 5 is a protrusion pressurized against the rotor 6, and is configured to vibrate together with the vibration of the piezoelectric characteristic member. When the friction member 5 is vibrated, the rotor 6 pressed against the friction member 5 rotates in a predetermined direction.

  The microcomputer 32 is configured to output to the D / A converter 34 a frequency instruction signal indicating the frequency of the voltage pulse waveform output from the A phase voltage pulse generation circuit 8 and the B phase voltage pulse generation circuit 10. Yes. The rotation speed of the rotor 6 of the piezoelectric actuator 2 is controlled by the frequency of the voltage pulse waveform. The microcomputer 32 is configured to output to the phase shifter 38 a normal inversion instruction signal that instructs normal rotation and inversion of the rotor 6. By this forward / reverse instruction signal, the phase relationship between the two drive signals output from the phase shifter 38 is changed, and the rotation direction of the rotor 6 is switched. Further, the microcomputer 32 generates an A-phase voltage pulse by generating a float period instruction signal indicating the length of the float period included in the voltage pulses output from the A-phase voltage pulse generation circuit 8 and the B-phase voltage pulse generation circuit 10. It is configured to output to the circuit 8 and the B-phase voltage pulse generation circuit 10. The voltage pulse float period will be described later.

  The D / A converter 34 is configured to convert a digital signal input from the microcomputer 32 into an analog signal. As described above, the digital signal input from the microcomputer 32 is a frequency instruction signal for indicating the frequency of the voltage pulse waveform, and the D / A converter 34 outputs an analog signal corresponding to the instructed frequency. It is configured as follows.

  The voltage controlled oscillator 36 is an oscillator whose oscillation frequency varies depending on the applied voltage, and outputs a rectangular wave (voltage pulse waveform) having a frequency corresponding to the voltage signal input from the D / A converter 34 to the phase shifter 38. Is configured to do.

The phase shifter 38 is configured to generate a voltage pulse waveform that is 90 ° out of phase with the voltage pulse waveform input from the voltage controlled oscillator 36. In the present embodiment, the phase shifter 38 outputs the voltage pulse waveform input from the voltage controlled oscillator 36 as it is to the B phase voltage pulse generation circuit 10 as a drive signal, and a 90 ° phase with respect to this waveform. The shifted voltage pulse waveform is output to the A-phase voltage pulse generation circuit 8 as a drive signal. In the present embodiment, the phase shifter 38 is a voltage pulse waveform that is output to the A-phase voltage pulse generation circuit 8 when “forward rotation” is instructed by the normal inversion instruction signal input from the microcomputer 32. The phase of the voltage pulse waveform is advanced by 90 °, and when “inversion” is instructed, the phase of the voltage pulse waveform is delayed by 90 °.
The phase difference between the A-phase and B-phase voltage pulses may be other than ± 90 °.

  The A-phase voltage pulse generation circuit 8 includes a switching element control circuit 12, a high-voltage power supply 14 that is a voltage source, a high-side switching element 16, a low-side switching element 18, and a coil 20.

  The switching element control circuit 12 is configured to switch the high-side switching element 16 and the low-side switching element 18 to a conductive state or a non-conductive state based on the ultrasonic band drive signal and the float period instruction signal. . Specifically, the switching element control circuit 12 can be configured by various logic ICs or the like.

  The high-voltage power supply 14 is a voltage source that generates a positive high voltage, and is connected to the high-side switching element 16. When the high-side switching element 16 is switched to the conductive state, a high voltage is applied to the drive element via the coil 20.

  In the present embodiment, the high-side switching element 16 is configured by an N-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), the gate terminal of which is connected to the switching element control circuit 12, and the drain terminal Is connected to the high-voltage power supply 14, and the source terminal is connected to the coil 20.

  In this embodiment, the low-side switching element 18 is composed of an N-channel type MOSFET, and has a gate terminal connected to the switching element control circuit 12, a drain terminal connected to the coil 20, and a source terminal grounded. Has been.

  The coil 20 is connected to the polarization part 4a via the drive terminal 20a which is the first terminal, and the second terminal 20b is the source terminal of the high-side switching element 16 and the low-side switching element 18 as described above. Connected to the drain terminal. Here, the polarization unit 4a connected to the coil 20 acts as an LC resonance circuit, and the inductance value of the coil 20 is selected so that an appropriate high voltage is generated at the drive terminal 20a in the vicinity of the resonance frequency of the piezoelectric actuator 2. Has been.

  The B-phase voltage pulse generation circuit 10 includes a high-voltage power supply 22 that is a voltage source, a high-side switching element 24, a low-side switching element 26, a coil 28, and a switching element control circuit 30. The B-phase voltage pulse generation circuit 10 is the same as the A-phase voltage pulse generation circuit 8 described above, and a description thereof will be omitted. In FIG. 1, the high-voltage power supply 14 and the high-voltage power supply 22 are illustrated separately, but they can also be configured from the same high-voltage power supply.

  Next, the operation of the A-phase voltage pulse generation circuit 8 built in the piezoelectric actuator driving circuit 3 will be described with reference to FIG. FIG. 2A shows the A-phase voltage pulse generation circuit 8 and FIG. 2B is a timing chart showing the operation of the A-phase voltage pulse generation circuit 8. The timing chart of FIG. 2B shows the drive signal, the state of the high-side switching element 16, the state of the low-side switching element 18, and the voltage of the second terminal 20b of the coil 20 in order from the top.

First, the switching element control circuit 12 receives a rectangular-wave drive signal shown in the upper part of FIG. The drive signal is selected to have a frequency close to the resonance frequency of the piezoelectric actuator 2, and an appropriate high voltage is generated at the drive terminal 20a.
As shown in FIG. 2B, when the drive signal is at the L level, the switching element control circuit 12 turns off the high-side switching element 16 (off) and turns on the low-side switching element 18 ( turn on. Specifically, the switching element control circuit 12 sends signals to the gate terminals of the high-side switching element 16 and the low-side switching element 18 to switch these FETs on and off. When the high-side switching element 16 is turned off and the low-side switching element 18 is turned on, the second terminal 20b of the coil 20 is grounded via the low-side switching element 18, and thus becomes 0V.

  Next, when the drive signal rises from the L level to the H level, the low-side switching element 18 is immediately switched off, and the high-side switching element 16 has a float period T1 corresponding to the float period instruction signal from the microcomputer 32. After the elapse, it is switched on. When the low-side switching element 18 is switched off and the high-side switching element 16 is switched on, the second terminal 20b of the coil 20 is connected to the high-voltage power supply 14 via the high-side switching element 16 and the second terminal 20b. The terminal voltage rises to the voltage of the high-voltage power supply 14.

  Here, both the low-side switching element 18 and the high-side switching element 16 are off during the float period T1 after the low-side switching element 18 is turned off until the high-side switching element 16 is turned on. During the float period T1 (shaded portion in FIG. 2B), the second terminal 20b of the coil 20 is electrically disconnected from the high-voltage power supply 14 and the ground potential, and is in a floated state. The voltage of the terminal 20b becomes a value depending on the potential of the drive terminal 20a, the current direction of the coil 2, and the current value within the range from the ground potential to the voltage of the high voltage power source due to the effect of the parasitic diode of the FET.

  Subsequently, when the drive signal falls from the H level to the L level, the high-side switching element 16 is immediately switched off, and the low-side switching element 18 is switched on after a predetermined float period T1 has elapsed. When the high-side switching element 16 is turned off and the low-side switching element 18 is turned on, the second terminal 20b of the coil 20 is grounded via the low-side switching element 18, and thus becomes 0V again.

  The second terminal 20b of the coil 20 is electrically connected to the high-voltage power supply 14 and the ground potential during the float period T1 from when the high-side switching element 16 is switched off to when the low-side switching element 18 is switched on. It will be separated from and will float. The float period T1 is also set to a length corresponding to the float period instruction signal.

  By repeating the above operation, only the high-side switching element 16 is turned on, and the high-side switching element 16 and the low-side switching element 18 are both turned off during the voltage application period in which voltage is applied to the second terminal 20b. The float period in which the potential of the second terminal 20b is floated and the ground period in which only the low-side switching element 18 is in a conductive state and the second terminal 20b is grounded are periodically switched, and the voltage pulse is polarized. Applied to the part 4a. That is, in the voltage application period, the high-voltage power supply 14 is connected to the polarization unit 4a via the coil 20, and in the ground period, the polarization unit 4a is connected to the ground potential via the coil 20, and in the float period, The polarization unit 4a is disconnected from the high-voltage power supply 14 and the ground potential and becomes a float potential. When the voltage pulse resonates with the inductance of the coil 20 and the capacitance component of the polarization portion 4a, a high pulse voltage is applied to the polarization portion 4a, and the piezoelectric characteristic member 4c is vibrated and deformed.

  The configuration and operation of the B-phase voltage pulse generation circuit 10 built in the piezoelectric actuator drive circuit 3 are the same as those of the A-phase voltage pulse generation circuit 8, and thus the description thereof is omitted. In the present embodiment, the B-phase voltage pulse generation circuit 10 is input with a rectangular wave that is 90 ° out of phase with the drive signal of the A-phase voltage pulse generation circuit 8. The voltage pulse generated by the voltage pulse generation circuit 10 is 90 ° out of phase with the voltage pulse generated by the A-phase voltage pulse generation circuit 8. The float period included in the voltage pulse waveform is set independently for the A-phase voltage pulse generation circuit 8 and the B-phase voltage pulse generation circuit 10 by the float period instruction signal input from the microcomputer 32. Accordingly, the float periods included in the voltage pulse waveforms respectively output from the two voltage pulse generation circuits are set to arbitrary lengths.

  Next, an example of a voltage pulse waveform output by the A-phase voltage pulse generation circuit 8 and the B-phase voltage pulse generation circuit 10 will be described with reference to FIG. FIG. 3A shows an example of a voltage pulse waveform when the rotor 6 of the piezoelectric actuator 2 is rotated forward, and FIG. 3B shows an example of a voltage pulse waveform when the rotor 6 is reversed. The voltage pulse waveform output from the A-phase voltage pulse generation circuit 8 indicates the voltage at the second terminal 20b of the coil 20, and the voltage pulse waveform output from the B-phase voltage pulse generation circuit 10 indicates the voltage of the coil 28. The voltage at the second terminal 28b is shown.

  As shown in FIG. 3A, in the present embodiment, when the rotor 6 is rotated forward, the voltage pulse waveform output from the A phase voltage pulse generation circuit 8 is output from the B phase voltage pulse generation circuit 10. The phase is advanced by 90 ° with respect to the output voltage pulse waveform. In the example shown in FIG. 3A, the A-phase float period is set longer than the B-phase float period.

  On the other hand, as shown in FIG. 3B, when the rotor 6 is reversed, the voltage pulse waveform output from the A-phase voltage pulse generation circuit 8 is changed to the voltage pulse output from the B-phase voltage pulse generation circuit 10. The phase is 90 ° behind the waveform. In the example shown in FIG. 3B, the A-phase float period is set shorter than the B-phase float period, contrary to the forward rotation shown in FIG.

  The float period included in the voltage pulse waveform is set to 5 to 25%, preferably 10 to 20% of one period of the voltage pulse waveform at both the rise and fall of the voltage pulse. Alternatively, the float period included in the voltage pulse waveform is set to 0.7 to 4 μsec, preferably 1.5 to 3 μsec, both when the voltage pulse rises and falls.

Next, with reference to FIG. 4 thru | or FIG. 8, the effect | action of the piezoelectric actuator apparatus 1 by embodiment of this invention is demonstrated.
FIG. 4 is a voltage pulse waveform when the float periods of the A-phase voltage pulse generation circuit 8 and the B-phase voltage pulse generation circuit 10 are the same, and the voltage and drive at the second terminal 20b of the coil 20 in order from the top. The voltage at the terminal 20a, the voltage at the second terminal 28b of the coil 28, and the voltage at the drive terminal 28a are shown. In this specification, such a voltage pulse waveform is referred to as a symmetrical float period waveform.

  FIG. 5 shows a voltage pulse waveform when the float period of the B-phase voltage pulse generation circuit 10 is made shorter than the float period of the A-phase voltage pulse generation circuit 8, and as in FIG. 4, the terminals 20b and 20a from the upper stage. , 28b, and 28a. In this specification, such a voltage pulse waveform is referred to as an asymmetric float period waveform.

  FIG. 6 shows, as a comparative example, voltage pulse waveforms in the case where neither the A-phase voltage pulse generation circuit 8 nor the B-phase voltage pulse generation circuit 10 has a float period. Similarly to FIG. 4, the terminals 20b and 20a , 28b, and 28a. In this specification, such a voltage pulse waveform is referred to as a conventional voltage pulse waveform.

  In general, a dead time is provided in a circuit in which two switching elements are connected in series between a voltage source and a ground potential, and these switching elements are switched to generate a voltage pulse waveform. This dead time is a period in which the two switching elements are simultaneously turned off in order to prevent the switching elements connected between the voltage source and the ground potential from being turned on at the same time and the voltage source and the ground potential from being short-circuited. Is provided. That is, when switching only the high-side switching element from the on state to the low-side switching element only, the high-side switching element is turned off first, and both switching elements are turned off. After that, the low-side switching element is turned on. Such a dead time when both the switching elements are turned off is unavoidably provided for normal operation of the circuit, and may be zero in order to output an accurate voltage pulse waveform. It is considered ideal. For this reason, in a circuit that has been put to practical use, the dead time is set to the minimum necessary length, and is usually set to a very short period of about 300 nsec.

  Also in the example shown in FIG. 6, the dead time is set to about 300 nsec. On the other hand, the float period in the embodiment of the present invention is the same as the dead time in that the high-side switching element and the low-side switching element are simultaneously turned off. However, the float period is positively provided to improve the control characteristics of the piezoelectric actuator 2, and the period is also set to several times the normal dead time. In the specification, this is called a float period for distinction.

  First, as shown in FIG. 4, the voltage pulse waveform at the second terminal 20b of the coil 20 is set to the ground potential during the ground period T3a in which only the low-side switching element 18 is turned on, while high-side switching is performed. In the voltage application period T2a in which only the element 16 is turned on, it is equal to the voltage of the high-voltage power supply 14. On the other hand, in the float period T1a located between the ground period T3a and the voltage application period T2a, the second terminal 20b is in a floated state, so that the second terminal 20b has the effect of the parasitic diode of the FET. In the range from the ground potential to the voltage of the high-voltage power supply, the potential of the drive terminal 20a of the coil 20, the current direction of the coil 20, and the potential depending on the current value are taken and changed in vibration.

  On the other hand, the voltage waveform of the drive terminal 20a of the coil 20 is generally a waveform having a high voltage during the voltage application period T2a and a low voltage during the grounding period T3a, but the coil 20 and the polarization unit 4a. Due to the resonance and the like, the waveform is complicated. This is because the potential of the second terminal 28b is within the range from the ground potential to the voltage of the high voltage power supply due to the effect of the parasitic diode of the FET, the potential of the drive terminal 28a of the coil 28, the current direction of the coil 28, and the current value. This is because a dependent potential is taken.

  Further, the voltage pulse waveform at the second terminal 28b of the coil 28 has the same tendency as the voltage waveform at the second terminal 20b, but the length of the set float period T1b is the same as the float period T1a. Nevertheless, the waveform during the float period T1b is different from that of the second terminal 20b. This is because the potential of the second terminal 28 b takes a potential depending on the potential of the drive terminal 28 a of the coil 28. The voltage waveform at the drive terminal 28a of the coil 28 has the same tendency as the voltage waveform at the drive terminal 20a, but is different from the voltage waveform at the drive terminal 20a.

  In the symmetrical float period waveform shown in FIG. 4, the float periods T1a and T1b are 1.52 μsec, the voltage application periods T2a and T2b and the ground periods T3a and T3b are 5.76 μsec.

Next, in the voltage pulse waveform shown in FIG. 5, the float period T1b by the B-phase voltage pulse generation circuit 10 is shorter than the float period T1a by the A-phase voltage pulse generation circuit 8. The waveform of the drive terminal 20a and the waveform of the drive terminal 28a are smoother and approach a sine wave.
In the asymmetric float period waveform shown in FIG. 5, the float period T1a is 2.92 μsec, the voltage application period T2a and the ground period T3a are 4.36 μsec, and the float period T1b is 1.24 μsec. The period T2b and the grounding period 3b are 6.04 μsec.

  Next, in the conventional voltage pulse waveform shown in FIG. 6 as a comparative example, the voltage pulse waveform at the second terminals 20b and 28b is an accurate rectangular wave in which the voltage application period T2 and the ground period T3 appear alternately. . In the voltage pulse waveform shown in FIG. 6, there is a dead time for turning off the high-side and low-side switching elements at the same time. However, since the dead time is extremely short compared to the float period, the influence is the voltage pulse waveform. It does not appear in

  On the other hand, in FIG. 6, the waveform of the drive terminal 20a and the waveform of the drive terminal 28a are more disturbed than the voltage waveforms shown in FIGS. In particular, at the moment when the potential of the second terminals 20b and 28b rises from the ground potential to the potential of the high voltage source, the potential of the drive terminal that has monotonously increased once decreases and then increases again. This is because in the comparative example in which no float period is provided, the potentials of the second terminals 20b and 28b are always constrained to the ground potential or the potential of the high voltage source. It seems that it is disturbed by the influence.

  On the other hand, in the example shown in FIG. 4 and FIG. 5, since a float period having a predetermined length is provided between the switching of the ground potential and the potential of the high voltage source, the second terminal 20b and 28b can take a free electric potential within the range of the voltage of a high voltage power supply from an earth electric potential. For this reason, it is considered that the potential of the drive terminal of each coil does not become a complicated waveform by being disturbed by the influence of the potential of the second terminal.

Next, a control result of the piezoelectric actuator 2 by the piezoelectric actuator drive circuit 3 according to the embodiment of the present invention will be described with reference to FIGS.
FIG. 7 is a graph showing the relationship between the number of rotations and the consumption current of the piezoelectric actuator drive circuit 3 when the rotor 6 of the piezoelectric actuator 2 that is an ultrasonic motor is rotated by the piezoelectric actuator drive circuit 3 of the present embodiment. . In the graph of FIG. 7, the result of driving the piezoelectric actuator 2 by the symmetrical float period waveform shown in FIG. 4 is shown by a thick solid line, the result by the asymmetric float period waveform shown in FIG. The result of the conventional voltage pulse waveform shown in FIG.

  As can be seen from FIG. 7, in the piezoelectric actuator drive circuit 3 of the present embodiment, when the piezoelectric actuator 2 is driven with a symmetric float period waveform and an asymmetric float period waveform, the current consumption is almost monotonically as the rotational speed increases. It can be seen that the number has increased. On the other hand, it can be seen that the drive with the conventional voltage pulse waveform shown in FIG. 6 consumes more current than the piezoelectric actuator drive circuit 3 of the present embodiment, and the drive efficiency of the piezoelectric actuator 2 is poor. Further, it can be seen that there is a region where the drive current becomes very large at a low rotational speed in the conventional driving with the voltage pulse waveform. As shown in FIG. 6, in the conventional voltage pulse waveform, there is a large variation in the voltage waveform appearing at the drive terminal, and it is considered that the efficiency is remarkably reduced in a specific frequency band.

  Furthermore, when the current consumption of the symmetrical float period waveform indicated by the thick solid line and the asymmetrical float period waveform indicated by the broken line are compared, the current consumption of both is similar, but in the high speed region, the asymmetrical float period waveform indicated by the broken line The current consumption is slightly higher. That is, in a predetermined high rotation speed region, it can be seen that the driving efficiency is better for the A-phase voltage pulse waveform and the symmetrical float period waveform in which the float periods included in the B-phase voltage pulse waveform are the same.

  FIG. 8 is a graph showing the relationship between the frequency of the voltage pulse waveform and the rotational speed when the rotor 6 of the piezoelectric actuator 2 is rotated by the piezoelectric actuator drive circuit 3 of the present embodiment. In the graph of FIG. 8, the result of driving the piezoelectric actuator 2 by the symmetric float period waveform shown in FIG. 4 is shown by a thick solid line, the result by the asymmetric float period waveform shown in FIG. The result of the conventional voltage pulse waveform shown in FIG.

  As shown in FIG. 8, the piezoelectric actuator 2 has a tendency that the number of rotations increases as the frequency of the voltage pulse waveform decreases. Therefore, when the piezoelectric actuator 2 is started from a stopped state, the frequency of the voltage pulse waveform is gradually decreased from a high frequency. As is clear from FIG. 8, the rotor 6 starts to rotate from the highest frequency of the voltage pulse waveform because the A-phase voltage pulse waveform and the B-phase voltage pulse waveform indicated by the broken lines are included in the float. It is an asymmetrical float period waveform with different periods. In the broken line graph, after the rotor 6 starts to rotate, the rotational speed increases almost monotonously with a decrease in the frequency of the voltage pulse waveform in the low speed region, so that the rotational speed of the rotor 6 is easily controlled. This is particularly advantageous when performing stop position control.

  It is a conventional voltage pulse waveform indicated by a thin solid line that the rotor 6 starts to rotate from the next highest frequency. However, the thin solid line graph has a region where the rotational speed decreases to almost zero while the frequency decreases. In other words, in the conventional voltage pulse waveform, when the piezoelectric actuator 2 is driven at a certain frequency, the rotor 6 may stop, and it is difficult to freely control the rotation speed of the rotor 6.

  In addition, the symmetrical float period waveform shown by the thick solid line in FIG. 8 does not start to rotate the rotor 6 to the lowest frequency, and the rotation speed when starting to rotate is higher than other waveforms, so in the low speed range. The controllability is inferior to that of the asymmetrical float period waveform, but after starting to rotate, the rotational speed monotonously increases with a decrease in frequency, indicating good controllability.

  As shown in FIG. 7, the drive efficiency of the piezoelectric actuator 2 is best controlled using the symmetrical float period waveform shown in FIG. Further, as shown in FIG. 8, the control using the asymmetric float period waveform shown in FIG. Therefore, by switching and executing the first control mode using the symmetric float period waveform and the second control mode using the asymmetric float period waveform, a further excellent piezoelectric actuator drive circuit 3 can be configured.

  In particular, the piezoelectric actuator 2 is activated in the second control mode using the asymmetric float period waveform shown in FIG. 5, and the voltage pulse waveform is lowered to a predetermined frequency to increase the rotation speed, and then shown in FIG. By controlling by switching to the first control mode using a symmetrical float period waveform, it is possible to realize good controllability and high driving efficiency.

  According to the piezoelectric actuator device 1 of the embodiment of the present invention, since the float period T1 is provided between the voltage application period T2 and the grounding period T3 (FIGS. 4 and 5), it is applied to the polarization units 4a and 4b. Therefore, the piezoelectric actuator 2 can be driven efficiently or smoothly.

  According to the piezoelectric actuator device 1 of the embodiment of the present invention, voltage pulses having different phases are applied to the polarization part 4a and the polarization part 4b of the piezoelectric actuator 2, respectively, so that a voltage pulse is applied only to a single polarization part. Compared to the case, the piezoelectric actuator 2 can be driven efficiently or smoothly.

  According to the piezoelectric actuator device 1 of the embodiment of the present invention, voltage pulses having different float periods can be applied to the polarization unit 4a and the polarization unit 4b. Appropriate driving can be performed.

  According to the piezoelectric actuator device 1 of the embodiment of the present invention, the first control mode using the symmetric float period waveform and the second control mode using the asymmetric float period waveform can be switched and executed. By switching the control according to the driving situation where the control mode is advantageous and the driving situation where the second control mode is advantageous, the piezoelectric actuator can be driven more efficiently and smoothly.

  According to the piezoelectric actuator device 1 of the embodiment of the present invention, after starting the ultrasonic motor in the second control mode with good startability, the startability and efficiency are improved by switching to the first control mode with good drive efficiency. Can be made.

  According to the piezoelectric actuator device 1 of the embodiment of the present invention, the float period that occupies about 10% of one period of the voltage pulse, which is much longer than the dead time included in the voltage pulse by the normal drive circuit, is provided. As a result, the drive efficiency of the piezoelectric actuator drive circuit can be sufficiently improved.

  According to the piezoelectric actuator device 1 of the embodiment of the present invention, the high-side switching elements 16 and 24 and the low-side switching elements 18 and 26 are connected to the polarization units 4a and 4b via the coils 20 and 28, respectively. A voltage higher than the voltage of the voltage sources 14 and 22 can be applied to the polarization units 4a and 4b by utilizing the resonance phenomenon caused by the coils 20 and 28. As described above, in the piezoelectric actuator drive circuit of the type in which the coil is connected between the switching element and the polarization unit, the output impedance of the drive circuit tends to increase due to the intervention of the coil, but the piezoelectric actuator of this embodiment According to the drive circuit, by providing a float period in the voltage pulse waveform, it is possible to efficiently drive the piezoelectric actuator while suppressing adverse effects such as electromotive force caused by the coil or using electromotive force caused by the coil.

  As mentioned above, although preferable embodiment of this invention was described, a various change can be added to embodiment mentioned above. In particular, in the above-described embodiment, the piezoelectric actuator drive circuit is used to drive the piezoelectric actuator that drives the rotor. However, the piezoelectric actuator drive circuit of the present invention can be used for any piezoelectric actuator such as a linear actuator. It can be applied to driving.

  In the above-described embodiment, the piezoelectric actuator drive circuit is configured to be capable of normal rotation and reverse drive. However, the present invention can also be applied to a piezoelectric actuator drive circuit capable of driving in only one direction. .

  Further, in the above-described embodiment, the piezoelectric actuator drive circuit applies the voltage pulse waveform having different phases to the two polarization parts. However, the present invention applies the voltage pulse waveform only to the single polarization part. You may apply to a piezoelectric actuator drive circuit.

  In the above-described embodiment, the coil is connected between the switching element and the polarization unit. However, the present invention can also be applied to a piezoelectric actuator drive circuit of a type in which no coil is provided.

  Furthermore, in the above-described embodiment, the drive element is driven using a positive high-voltage power supply, but a negative high-voltage power supply can also be used as the high-voltage power supply. In the above-described embodiment, the N-channel MOSFET is used as the switching element. However, in consideration of the polarity of the high-voltage power supply, a P-channel MOSFET can be used as the switching element.

  In the above-described embodiment, a piezoelectric actuator having a plurality of polarization portions formed in a single piezoelectric characteristic member is controlled. However, the polarization portions are divided into multiple layers, and ground electrodes and drive electrodes are alternately stacked. The present invention can be applied to various actuators such as the above-described type of piezoelectric actuator.

Furthermore, in the above-described embodiment, the symmetric float period waveform and the asymmetric float period waveform always have a constant float period. However, as a modification, the float period may be changed during driving of the piezoelectric actuator. it can. For example, in the symmetric float period waveform, it is possible to control the float period to be extended or shortened during driving while maintaining the same A phase and B phase float periods.
Further, the third control mode in which the float period is changed during driving, the first control mode using the symmetric float period waveform, and the second control mode using the asymmetric float period waveform are switched as appropriate and executed. You can also.

DESCRIPTION OF SYMBOLS 1 Piezoelectric actuator apparatus 2 Piezoelectric actuator 3 Piezoelectric actuator drive circuit 4a, 4b Polarization part 5 Friction member 6 Rotor 8 A phase voltage pulse generation circuit 8
10 B-phase voltage pulse generation circuit 10
12 Switching element control circuit 14 High voltage power supply (voltage source)
16 High-side switching element 18 Low-side switching element 20 Coil 20a Drive terminal 20b Second terminal (first terminal)
22 High voltage power supply (voltage source)
24 High-side switching element 26 Low-side switching element 28 Coil 28a Drive terminal (first terminal)
28b Second terminal 30 Switching element control circuit 32 Microcomputer 34 D / A converter 36 Voltage controlled oscillator 38 Phase shifter

Claims (6)

A piezoelectric actuator drive circuit that includes a plurality of polarization units and that drives a piezoelectric actuator to which a drive voltage is applied to the plurality of polarization units,
A voltage source;
A high-side switching element connected between the polarization unit and the voltage source and switched between a conductive state and a non-conductive state by a control signal;
A low-side switching element that is connected between the polarization part and the ground potential and is switched between a conductive state and a non-conductive state by a control signal;
The high-side switching element and the low-side switching element are controlled so that only the high-side switching element is in a conductive state and the voltage source is connected to the polarization unit, the high-side switching element and the low-side switching element A floating period in which all the switching elements are in a non-conductive state, and the polarization unit is disconnected from the voltage source and the ground potential, and a ground period in which only the low-side switching element is in a conductive state and the polarization unit is connected to the ground potential. by periodically switching by applying a voltage pulse to the polarized portion, have a, a switching element control circuit for driving the piezoelectric actuator,
The switching element control circuit applies voltage pulses having different phases to the plurality of polarization units, and applies voltage pulses having different float period lengths to the polarization units. Actuator drive circuit. The switching element control circuit includes a first control mode in which a voltage pulse applied to each polarization unit includes a float period having the same length, and a voltage pulse applied to each polarization unit includes a float period having a different length. The second control mode is switched, or the voltage pulse applied to each polarization unit is switched between the third control mode including a float period in which the length is changed during driving of the piezoelectric actuator, and the second control mode. the piezoelectric actuator drive circuit according to claim 1, wherein the run. The piezoelectric actuator is an ultrasonic motor, and the switching element control circuit executes the second control mode when the ultrasonic motor is activated, and then the first motor when the ultrasonic motor reaches a predetermined number of rotations. The piezoelectric actuator drive circuit according to claim 2 , wherein the piezoelectric actuator drive circuit is switched to a control mode. The float period, the piezoelectric actuator drive circuit according to any one of claims 1 to 3 accounted for 5% or more of the voltage pulse one cycle to be applied. Further comprising a coil for generating a high voltage to the polarized portion, the high-side switching element and the low-side switching elements, of claims 1 to 4 via the coil are connected to the polarized portion The piezoelectric actuator drive circuit according to any one of the preceding claims. With the rotor,
A stator having a plurality of polarization portions for driving the rotor;
The piezoelectric actuator drive circuit according to any one of claims 1 to 5 , wherein a drive voltage is applied to at least one of the plurality of polarization units.
A piezoelectric actuator device comprising:

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